Activated carbon materials in the form of granules or powders are used for a variety of pollution control applications. Pollutants in liquid or gas streams are removed by contacting the stream with activated carbon in granulated or powdered form. The fine angstrom size pore structure of activated carbon enables adsorption of the impurities out of the process streams. The pores in activated carbon which impart the unique ability to adsorb the pollutants even at very low concentrations (e.g., as low as 1 ppm) are in the 5 to 20 angstrom range. Pores above about 50 angstroms do not contribute significantly to adsorption at low concentrations.
Although activated carbon is used in many pollution control applications, in the form of pellets or powder, a major disadvantage with this form of carbon is the high pressure drop associated with packed beds of pellets or powder. Another problem is that of entrainment of the powder in the flow stream and attrition of the granules. One way around this problem is to form the activated carbon in the shape of a honeycomb. The honeycomb geometry has the advantage of high geometric surface area available for contact and low pressure drop across the bed. In some industrial processes honeycomb geometries are necessary.
Resins have been used in making carbon bodies both as binders and as carbon precursors. For example, phenolic resins are extruded into honeycomb shapes as in U.S. Pat. No. 4,399,052. The resin is cured, carbonized, and activated. A major difficulty with such a product is that during carbonization when about 50 wt. % is lost, such bodies distort and crack in many cases.
All of the above difficulties are overcome by the process of coating a porous ceramic honeycomb body with a thermosetting resin, and then carbonizing and activating. Such products are described in U.S. application Ser. No. 08/11,385, filed Jan. 29, 1993. The drawbacks associated with this process are the cost of first extruding and then firing a ceramic honeycomb and then coating, curing, and activating. Secondly the amount of resin and hence the amount of carbon that can be put on the body is limited, thus limiting its capacity.
Methods of making shapes by dipping rods or cylinders in resin and then forming honeycombs by removing the rods after curing the resin as in U.S. Pat. Nos. 3,825,460 and 3,922,412, again are subject to the same type of problems such as warping and cracking as the bodies formed by extrusion of resin.
It would be highly desirable to have a method in which the adsorption capacity per unit volume can be controlled so that it can be made to fit the requirements of a specific application and at the same time exhibit properties in the body of no attrition, minimized pressure drop, and high surface area in a given volume.
The present invention provides such a carbon structure and a method of making it.